要求：

模擬實現c++庫函式裡面string的部分功能，實現增刪查改，比較預算符的過載

#ifndef __MySTRING_H__
#define __MYSTRING_H__

#define _CRT_SECURE_NO_DEPRECATE 1
#include<iostream>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
using namespace std;

class String
{
public:
	String(const char* str)
		:_str(new char[strlen(str)+1])
		,_size(strlen(str)+1)
		,_capacity(_size)
	{
		strcpy(_str,str);
	}
	String(const String& d)
		:_str(new char[strlen(d._str)+1])
		,_size(d._size)
		,_capacity(d._capacity)
	{
		strcpy(_str,d._str);
	}
	~String()
	{
		delete[] _str;
		_str = NULL;
		_size = 0;
		_capacity = 0;
	}

	//s1 = s2
	//1構造一個和目標物件一樣的物件
	//然後交換兩個物件
    void Swap(String& d) 
	{
		char* tmpchar = this->_str;
		this->_str = d._str;
		d._str = tmpchar;
	
		size_t tmpsize = this->_size;
		this->_size = d._size;
		d._size = tmpsize;
	
		size_t tmpcapacity = this->_capacity;
		this->_capacity = d._capacity;
		d._capacity = tmpcapacity;
	}

	String& operator=(const String& d)
	{
		if(_str == d._str)
		{
			return *this;
		}
		String tmp(d._str);
		Swap(tmp);
		return *this;
	}
char* GetStr()
{
	return _str;
}
void Expand(size_t inc);
void PushBack(char ch);
void PushBack(char* str);
void PopBack();
void Insert(size_t pos, char ch) ;
void Insert(size_t pos, const char* str); 
void Erase(size_t pos, size_t count);
int Find(char ch)const;
int Find(const char* str) const; 
bool operator==(const String& s) const;
bool operator!=(const String& s)const;
bool operator>(const String& s) const; 
bool operator>=(const String& s) const; 
bool operator<(const String& s) const; 
bool operator<=(const String& s) const;
char& operator[](size_t pos);
private:
	char* _str;
	size_t _size;
	size_t _capacity;
};

void String:: Expand( size_t inc)
{
		_str = (char*)realloc(_str,_size+inc);
	   if(_str == NULL)
	   {
			perror(_str);
	   }
	   _capacity += inc;
	   //cout<<"haha"<<endl;
}


 void String:: PushBack(char ch )
{
	if(_size == _capacity)
	{
		Expand(1);
	}
	_str[strlen(_str)] = ch;
	_str[_size] = '\0';
	++_size;
}
 void String:: PushBack(char* str )
 {
	Expand(strlen(str));
	strcpy((_str+_size-1),str);
	_size+= strlen(str);
 }
void String:: PopBack()
{
	assert(strlen(_str)>=1);
	_str[strlen(_str)-1] = '\0';
	--_size;
}
void String:: Insert(size_t pos, char ch)
{
	if(_size == _capacity)
	{
		Expand(4);
	}
	int i = 0;
	while(_size-i > pos)
	{
		_str[_size-i] = _str[_size-i-1]; 
		i++;
	}
	_str[pos] = ch;
	++_size;
}
//0位置有問題
void String:: Insert(size_t pos, const char* str)   
{
	int len = strlen(str);
	int end = strlen(_str);
	int i = 0;
	Expand(strlen(str)); 
	while(end >= (int)pos)       //把pos以後的資料統一向後移動len個單位
	{
		_str[end+len] = _str[end];
		--end;
	}
	while (*str)            //把資料放進去
	{
		_str[pos++] = *str++;
	}

	_size += len;
}
//1沒有資料或者超出範圍
//2在正常的範圍內
//依次向前覆蓋一個單位資料
void String:: Erase(size_t pos, size_t count)  //刪除pos位置開始的count個數據
{
	assert(pos<=_size-1);
	while(_str[pos+count-1])
	{
		_str[pos-1] = _str[pos+count-1];
		pos++;
	}
	_str[pos-1] = '\0';
	_size -=count;
}
//返回下標 從0開始
//1不存在字串
//2字串中不存在字元
//3字元傳中存在字元
int String:: Find(char ch) const
{
	assert(strlen(_str)!=0);
	int count = 0;
	char* tmpptr = _str;
	while(*tmpptr != '\0' )
	{
		if(*tmpptr != ch)
		{
			count++;
		}
		else
		{
			return count;
		}
		tmpptr++;
	}
	return -1;               //沒找打
}
//返回下標從0開始
int String:: Find(const char* str) const //尋找字串子串
{
	assert(strlen(_str)>0 && str!=NULL && strlen(str)>0 );
	char* tmp_str = _str;
	char* tmpstr = (char*)str;

	char* tmp;
	int count = 0;
	while(*tmp_str)
	 {
		if(*tmp_str != *tmpstr)
		{
			*tmp_str++;
			count++;
		}
		else
		{
			tmp = tmp_str; // 儲存父串的位置
			while(*tmp_str == *tmpstr && *tmp_str!= '\0' )
			{
				tmpstr++;
				tmp_str++;
			}
			if(*tmpstr == '\0')
			{
				return count;
			}
			tmp_str = tmp+1; 
		}
	}
		return -1;
}
bool String:: operator==(const String& s) const
{
	char* tmp_str = _str;
	char* tmpstr = s._str;

	while(*tmp_str == *tmpstr && *tmpstr != '\0' && *tmp_str != '\0')
	{
		tmp_str++;
		tmpstr++;
	}
	if( *tmpstr == '\0' && *tmp_str == '\0')
	{
		return true;
	}
	return false;
}

bool String:: operator!=(const String& s)const
{

	return !operator==(s);
}
bool String:: operator>(const String& s) const
{
	assert(strlen(_str)>=1 && strlen(s._str)>=1);

	char* tmp_str = _str;
	char* tmpstr = s._str;

	while(*tmp_str && *tmpstr)
	{
		if(*tmp_str>*tmpstr)
		{
			return true;
		}
		else if(*tmp_str<*tmpstr)
		{
			return false;
		}
		else
		{
			tmp_str++;
			tmpstr++;
		}
	}
	if(*tmp_str != '\0' )
	{
		return true;
	}
	return false;

}

bool String:: operator<(const String& s) const
{
	assert(strlen(_str)>=1 && strlen(s._str)>=1);
	return !(operator>(s) || operator==(s));
}

bool String:: operator<=(const String& s) const
{
	assert(strlen(s._str)>=1 && strlen(_str)>=1);
	return !(operator>(s));
}

bool String:: operator>=(const String& s) const
{
	assert(strlen(_str)>=1 && strlen(s._str)>=1);
	return !(operator<(s));
}

char& String:: operator[](size_t pos)
{
	assert(pos<=strlen(_str));
	
	return *(_str+pos);
}


#endif//__MySTRING_H__